We have been studying the biological properties of neuropathic strains of human immunodeficiency virus (HIV-1). This work indicates that some HIV-1 isolates from patients with neurological disorders do not kill T4 lymphocytes, despite the fact that they replicate effectively and were from patients with primarily neuropathic disorders. We have also initiated the molecular characterization of these isolates and their comparison with other HIV-1 (immunopathic isolates). In addition to these studies with neuropathic strains of HIV-1, we are involved in defining the potential antiviral properties of rifabutin against HIV-1.